In recent years, denser storage capacity and higher performance have grown in hard disk drives because of the increase in the volume of information used on personal computers and the expansion of applications to video recording devices, car navigation systems, and so on. The adoption of a perpendicular magnetic recording medium that achieves stable read output without thermal fluctuation in a high recording density area and a tunneling magnetoresistance head greatly contributes to the background. In the perpendicular magnetic recording medium, small unit magnets arrayed vertically on a magnetic recording medium surface are structured to be separated in advance by a non-magnetic material contained in a magnetic film.
Currently, as a proposal to control this separation area more actively and improve the magnetic recording density, a discrete track medium on which separation processing is done between disk tracks, as described in Japanese Patent Publication No. 2004-164692 (“Patent Reference 1”), and a bit patterned medium on which separation processing is done also in the direction of recording bits have been researched and developed. In both cases, the technique of forming and processing the separation area is a key point of high recording density. For example, for the discrete track medium, a substrate processing method in which grooves and lands are formed concentrically on the substrate in advance and a magnetic film is formed thereon, and a magnetic film processing method in which a magnetic film is masked and a part to be grooved is etched, thereby forming grooves and lands, have been proposed as techniques of forming and processing the separation area. However, since these techniques have many process steps of refilling the grooves with a non-magnetic material, then flattening its surface to the height of the magnetic film to be the lands, and forming a protection film on the flattened surface, additional problems arise such as an increase of particles generated on the surface of the magnetic film and the protection film, and an increase in surface roughness. This obstructs the narrowing of spacing (nano-spacing) between the magnetic head and the magnetic disk surface, which is another point for high recording density.
As a measure to solve these issues, a method that achieves magnetically the same effect as grooves and lands has been tried, instead of forming grooves and lands in terms of shape. This is an ion beam processing method in which a conventionally formed magnetic film is masked and ion implantation is carried out to a part to be grooved by using ion beams, thereby forming a non-magnetized area, as described in Japanese Patent Publication No. 2002-288813 (“Patent Reference 2”). As this technique is used, it is not necessary to later refill the grooves with a non-magnetic material and the flattening of its surface is not necessary, either. It is considered that good flying characteristics and magnetic characteristics as a magnetic recording medium are provided.
The problem to be solved by the present invention is associated with the ion beam processing method, which is one of the conventional techniques. That is, as made clear in an experiment by the inventors, it has been found that in the case where only ion implantation with ion beams is carried out, production of a uniform non-magnetic area over the surface of a magnetic disk substrate to be processed, and production of an accurate non-magnetic area according to the mask dimension are imperfect, and that local breakdown of the magnetic film is caused in the worst case.
For example, in the case where the substrate surface is irradiated with ion beams having general positive charges, the substrate itself gets easily charged up when the substrate is electrically floating. In this case, the substrate gets charged up with a voltage equivalent to the acceleration voltage of the ions, and ion implantation itself becomes difficult. Also, even when the substrate is electrically grounded, a local charged-up area is generated on the outermost surface of the substrate. Again, as a part where generation of ion implantation is difficult, ion implantation becomes non-uniform on the substrate surface as a whole. Particularly, if local charge-up occurs in an unmasked ion implantation area for the purpose of non-magnetization, the direction of ion implantation changes and ion implantation into other areas than the required non-magnetization area occurs. Thus, the mask pattern cannot be accurately transferred.
Also, usually, a disk substrate is held in point contact at several points in a deposition apparatus in most cases. Incident ions easily concentrate at these point-contact parts having an acute-angled shape, and the disk substrate including a magnetic medium may be broken because of the concentration of an electric field. This phenomenon occurs more conspicuously in the case where a base substrate of a non-conductive material, for example, glass and so on, is used. It is considered that this is because, while a conductive material such as a magnetic material is usually formed on a glass substrate, the thickness of its film is about a few ten to a few hundred nanometers and a sufficient current route sectional area cannot be secured in the direction of the film thickness.